Return to KLUBNL.PL main page

rsgb_lf_group
[Top] [All Lists]

Re: LF: RE: Analog oscillators

To: <[email protected]>
Subject: Re: LF: RE: Analog oscillators
From: "James Moritz" <[email protected]>
Date: Fri, 6 Jul 2012 00:45:25 +0100
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=btopenworld.com; s=s1024; t=1341531920; bh=lxls8VCaATxpLC87DjRD8kBSjHMRt6jrxyPaP57hrKA=; h=X-Yahoo-Newman-Property:X-YMail-OSG:X-Yahoo-SMTP:Received:Message-ID:From:To:References:In-Reply-To:Subject:Date:MIME-Version:Content-Type:Content-Transfer-Encoding:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE; b=vcElv44fvQTD0MvpIu2qqlZmS/yjb9+KJwxO0kK8ESmpMc5oIsDwanVzypynUTH5GiP1LlCFegzq6WlDMprF5/GZ9sjq9bh8+TqvmioWcTBU8pENtRRMjVkteEl3CTNQoj1HFV1DSTjVoOCpjgboYzwGw5ltuvA57xaKH8WhMNM=
Domainkey-signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=btopenworld.com; h=DKIM-Signature:X-Yahoo-Newman-Property:X-YMail-OSG:X-Yahoo-SMTP:Received:Message-ID:From:To:References:In-Reply-To:Subject:Date:MIME-Version:Content-Type:Content-Transfer-Encoding:X-Priority:X-MSMail-Priority:X-Mailer:X-MimeOLE; b=5Uj+yt6P/2Zrgri0dTTfwAkkJa0/RAWeWYVweNBUVM3kK7oj5t/uMbAWjM8Tih3YFDL8p96/1h+Kc0DJkXoexPYVdhnx1vwGRbnk/2bZifBV4F7ixs1htjdtH0ydho2X1MUcDgASNr98MmSz0FoZA0gAPf5bdV0KrueQIx+4A34= ;
In-reply-to: <[email protected]>
References: <[email protected]> <7E7DFBB4D102A04DB5ADC88D66628A4A0FAB99CC@ICTS-S-MBX5.luna.kuleuven.be> <[email protected]> <[email protected]> <op.wgzqhb2nyzqh0k@pc-roelof> <[email protected]>
Reply-to: [email protected]
Sender: [email protected]

Dear Stefan, LF Group,

In my experience, the oscillator circuit topology is usually less important than the component values used, the type of components, setting the bias current in the transistor, etc.

It is a bit disapointing. The oscillator is drifting several 100 Hz when looking to the divide by 4 side, i.e. the PA output i.e. close to 475 kHz.

I used 9 turns on a FT37-43.

I suspect this inductor may be the problem. The temperature coefficient of the permeability of ferrite is high, so the inductance will drift a lot with temperature. Also, the Q of ferrite cored inductors is usually rather low, with the effect of requiring higher transistor gain to make it oscillate, and greater loading of the resonant circuit by the transistor as a result. I suggest using a Txx-2 iron dust core insted of the -43 ferrite. It will need many more turns, but the inductance will be much more stable and the Q much higher. The higher Q will enable you to reduce the bias current in the oscillator transistor, and/or increase the shunting capacitor values. This will reduce the loading caused by the transistor.

Another way to increase stability is to reduce the operating frequency - an oscillator at 475kHz or 950kHz will tend to be more stable because the larger fixed capacitance values will mean the junction capacitance of the transistor will have less effect.

Cheers, Jim Moritz
73 de M0BMU




<Prev in Thread] Current Thread [Next in Thread>